Papers by maria victoria molina zambrana
Nuclear Physics B, 2005
Exclusive electroproduction of φ mesons has been studied in e ± p collisions at √ s = 318 GeV wit... more Exclusive electroproduction of φ mesons has been studied in e ± p collisions at √ s = 318 GeV with the ZEUS detector at HERA using an integrated luminosity of 65.1 pb −1 . The γ * p cross section is presented in the kinematic range 2 < Q 2 < 70 GeV 2 , 35 < W < 145 GeV and |t| < 0.6 GeV 2 . The cross sections as functions of Q 2 , W , t and helicity angle θ h are compared to cross sections for other vector mesons. The ratios R of the cross sections for longitudinally and transversely polarized virtual photons are presented as functions of Q 2 and W . The data are also compared to predictions from theoretical models.
Nuclear Physics B, 2005
Deep inelastic scattering and its diffractive component, ep → e ′ γ * p → e ′ XN, have been studi... more Deep inelastic scattering and its diffractive component, ep → e ′ γ * p → e ′ XN, have been studied at HERA with the ZEUS detector using an integrated luminosity of 4.2 pb −1 . The measurement covers a wide range in the γ * p c.m. energy W (37 -245 GeV), photon virtuality Q 2 (2.2 -80 GeV 2 ) and mass M X . The diffractive cross section for M X > 2 GeV rises strongly with W ; the rise is steeper with increasing Q 2 . The latter observation excludes the description of diffractive deep inelastic scattering in terms of the exchange of a single Pomeron. The ratio of diffractive to total cross section is constant as a function of W , in contradiction to the expectation of Regge phenomenology combined with a naive extension of the optical theorem to γ * p scattering. Above M X of 8 GeV, the ratio is flat with Q 2 , indicating a leading-twist behaviour of the diffractive cross section. The data are also presented in terms of the diffractive structure function, F D(3) 2 (β, x I P , Q 2 ), of the proton. For fixed β, the Q 2 dependence of x I P F D(3) 2 changes with x I P in violation of Regge factorisation. For fixed x I P , x I P F D(3) 2 rises as β → 0, the rise accelerating with increasing Q 2 . These positive scaling violations suggest substantial contributions of perturbative effects in the diffractive DIS cross section.
Nuclear Physics B, 2005
Inclusive jet cross sections in photoproduction for events containing a D * meson have been measu... more Inclusive jet cross sections in photoproduction for events containing a D * meson have been measured with the ZEUS detector at HERA using an integrated luminosity of 78.6 pb −1 . The events were required to have a virtuality of the incoming photon, Q 2 , of less than 1 GeV 2 , and a photon-proton centre-ofmass energy in the range 130 < W γp < 280 GeV. The measurements are compared with next-to-leadingorder (NLO) QCD calculations. Good agreement is found with the NLO calculations over most of the measured kinematic region. Requiring a second jet in the event allowed a more detailed comparison with QCD calculations. The measured dijet cross sections are also compared to Monte Carlo (MC) models which incorporate leading-order matrix elements followed by parton showers and hadronisation. The NLO QCD predictions are in general agreement with the data although differences have been isolated to regions where contributions from higher orders are expected to be significant. The MC models give a better description than the NLO predictions of the shape of the measured cross sections.
Physics Letters B, 2005
A search for pentaquarks decaying to Ξ-π- (Ξ-π+) and corresponding antiparticles has been perform... more A search for pentaquarks decaying to Ξ-π- (Ξ-π+) and corresponding antiparticles has been performed with the ZEUS detector at HERA. The data sample consists of deep inelastic ep scattering events at centre-of-mass energies of 300 and 318 GeV, and corresponds to 121 pb-1 of integrated luminosity. A clear signal for Ξ0(1530)→Ξ-π+ was observed. However, no signal for any new baryonic state was observed at higher masses in either the Ξ-π- or Ξ-π+ channels. The searches in the antiparticle channels were also negative. Upper limits on the ratio of a possible Ξ3/2-- (Ξ3/20) signal to the Ξ0(1530) signal were set in the mass range 1650 2350 MeV.
El sindicalismo en la época de la fundación de nuestro país 1825 no fue un tema relevante en aque... more El sindicalismo en la época de la fundación de nuestro país 1825 no fue un tema relevante en aquella revolución. Uno de los cambios relacionados con el tema laboral que se tuvo en aquella época por el año 1826 fue el reglamento para la explotación de minas . En el cual su función era la intervención de las relaciones entre el capital y el trabajo.
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Papers by maria victoria molina zambrana